The reason why the Chassidish and Yeshivish communities will never be part of it
Agudah put out a statement encouraging people to go, and I've seen self identified yeshivish people promoting it.
Chabad Chassidim are joining in individual capacities albeit without any official chabad organization lending its name to the march.
As stated above, I wasn't sure myself if I should go, in part because of some of what you say here. I'm not going to be singing hatikvah or waving an Israeli flag. I've never been to a "pro Israel march before.
I do believe you are wrong about the communities who will not join, and many many more from these communities will join than you think. The American politicians who this is supposed to impress do not need to know about the nuances of the religious Jews' fight against Zionism. What matters is its that Jewish lives in Israel and around the world are protected, and American law makers have a hand in that, bderech hatevah.
The notion that multiple bus loads would be going from Crown Heights to a Federation march would have been laughable just a few weeks ago.